The present invention relates generally to coating apparatus and methods, and more particularly, to an apparatus and method for cleaning the surface of an article while the article is in a region of extreme high vacuum, transferring the article to a second high vacuum region, where a part or all of the article may be coated by cathodic sputtering, moving the article to an adjoining, evacuated chamber for coating at least a part of the remainder of the article, or for adding a second coating to the coating first placed on the article, and removal of the article into a vacuum lock chamber which is provided to prevent atmospheric contamination of the articles or of portions of the coating and cleaning chambers.
The use of cathodic radio frequency induced sputtering using one or two target plates and an electrically biased article as the substrate, and other similar coating methods generally referred to as sputtering methods, have recently been of increasingly great interest to many industries. The reason for the interest taken in such apparatus and methods is that these techniques provide, for the first time on a commercial scale, methods of placing extremely fine, strongly adherent, very uniform coatings in extremely thin layers or films.
For example, it has recently become possible to coat the edge of cutting instruments with desired coating materials, such as refractory metals and alloys, corrosion resisting metals and alloys, plastic coatings for lubrication or other purposes, and the like. Use of sputtering methods to achieve coatings such as these is highly advantageous since the coatings are so thin that it is possible to coat the cutting edge of an instrument after it has been finish ground and honed without perceptibly decreasing the sharpness thereof. Continuous coatings, that is, coatings totally free of voids, "pock marks", inclusions or other discontinuities, may be applied in thicknesses of from 1,000 Angstoms down to as little as 50 Angstroms or less, and typically fall in the range of about 100 Angstroms in the case of coating of metals such as chromium and the like. Coatings of this order of magnitude, that is, of only about 1/100th of a micron, add some mechanical strength to the cutting edge of the instrument, and greatly increase corrosion resistance. Cutting edges such as these can then be post-treated with a lubricating material such as tetrafluoroethylene polymer waxes or other lubricous organic coatings.
As an example, razor blades having a pure chromium metal coating overlying their cutting edges have demonstrated noticeably greater useful life than corresponding uncoated edges. As pointed out above, these coatings are extremely thin, and accordingly, the cost of material used to place these coatings on blades is not great. However, as is the case with many coatings of such a thin cross section, uniformity and adhesion are of great importance. Sputtering systems by their very nature tend to produce a very even, continuous film; however, in the event that the substrate or surface of the article to be coated is chemically contaminated or has otherwise undergone significant alteration in texture or makeup after being prepared for application of the sputtered coating, the bond between the sputtered coating material and the article surface or substrate may lack the requisite strength and continuity.
Since, as pointed out above, sharpening cutting edges involves the use of honing the edge with fine grinding wheels and strops, there is significant opportunity for surface contamination, such as inclusion of foreign matter, to occur. In addition, abrasive particles, oils or other lubricants, as well as oxidation from exposure to the atmosphere may also occur on a finish ground or honed blade edge. Besides the sources of contamination referred to above, other airborne contaminants may contact the blade edge after sharpening.
Accordingly, particularly in view of the short time required for oxidation of freshly cut metal edges in the presence of atmospheric oxygen, it is highly desirable to protect cutting edges from the time they are formed until a relatively impervious coating can be applied thereto.
Thus, an apparatus and methods capable of cleaning a previously sharpened edge, and maintaining it in a substantially perfectly clean condition until coating it in the same apparatus would represent a worthwhile advance in the coating art, particularly in the area of quality control and product reliability and uniformity.
Accordingly, an object of the present invention is to provide an improved coating apparatus for cleaning and coating various articles.
A further object is to provide a method of cleaning an article and coating it before it has had an opportunity to become contaminated after being cleaned.
A still further object is to provide an apparatus in which a plurality of articles may be treated at successive treatement stations by cleaning and coating under high vacuum conditions.
Another object is to provide a method of vacuum cleaning and coating an article, by the utilization of high vacuum techniques including glow discharge, reverse sputtering, or sputter etching followed by sputter coating of an article to be coated, all without exposure of the article to the atmosphere intermediate the cleaning and coating steps.
Another object is to provide an apparatus having a plurality of chambers, at least one for cleaning, one for coating and one for serving as a vacuum lock so that articles may be transferred successively from one chamber to another without being contaminated during cleaning and coating.
A still further object is to provide an apparatus having a plurality of chambers, at least one for cleaning and one for coating, in which each chamber has separate means associated therewith for evacuating such chamber and in which several of the chambers have associated therewith means for leaking inert gas into a region across which a high frequency alternating potential or a direct current potential exists within the chambers.
Another object is to provide an apparatus having a plurality of adjacent chambers, at least one for cleaning and one or more for coating, in which the chambers are connected by gate or valve mechanisms allowing each chamber to be isolated from the other in one operational mode, and allowing spatial communication between at least two of the chambers in another operational mode.
Another object is to provide an apparatus as set forth above which is useful in cleaning and coating by different but related methods, and which can be made to perform a variety of different operations merely by alteration of the external vacuum and electrical circuitry associated therewith.
A still further object is to provide a cleaning and coating apparatus making possible higher volume production of cleaned and coated articles.
Another object is to provide a method of cleaning and coating an article which includes a glow discharge, sputter etching, or reverse sputtering cleaning step in one chamber, movement of the article through a valve to a second chamber which is then isolated from the first chamber and wherein at least a part of a coating is applied to the article, and subsequent removal of the coated article from the coating chamber through a vacuum lock for isolating the coating chamber from the atmosphere.
The present invention achieves these and other of its objects by providing a multi-chamber apparatus including valve means for isolating one chamber from another, means for permitting movement of articles between chambers, means for establishing a vacuum in each chamber and means for establishing an electrical connection between an outside power source and one or more electrodes within certain of the chambers; and by providing a method which includes placing articles in a first chamber, evacuating the chamber, cleaning the articles by glow discharge, reverse sputtering or sputter etching, moving the articles successively to one or more adjacent chambers for coating without exposing the articles to the atmosphere intermediate the cleaning and one or more of the coating steps, and removing the coated articles through a vacuum lock. The exact manner in which the invention achieves these objects will become more clear when reference is made to the following detailed description, to the appended claims, and to the accompanying drawings, in which like reference numerals indicate corresponding parts throughout.